If you're one of those many who thinks that with Yahoo! Search transitioning certain back-end functions to Microsoft, Yahoo!'s are no longer a "search engine." Please read what's Shashi Seth saying:
"People who assume that search is only about indexing, crawling and relevance of web documents are mistaken. First of all, there're hundreds of sources of data other than web index. Yahoo! Search supplements Microsoft's web Index with Yahoo!'s own content, content from 3rd-party relationships, and content from social networks like Twitter. We still maintain technology, science, scale and infrastructure required to crawl, index and rank this data – and all in real-time (less than a second).
Beyond that, Yahoo! is investing in many areas that'll redefine and reshape search – "we're still a search engine, and in a strong second place" in this very competitive marketplace. Watch out for amazing stuff coming from this search engine!"